NEW YORK (CNN) -- The body of a woman who authorities say was impaired by marijuana and alcohol when she caused a deadly head-on collision shows no signs of long-term alcohol use, according to an investigator hired by her family.

"I have looked at the autopsy, and the pancreas, liver and esophagus were clear," Tom Ruskin, lead investigator and president of CMP Protective and Investigative Group, told CNN. "I've never seen a case like this. No one has seen this woman drunk and we have interviewed over 50 people -- relatives, friends, colleagues and former employees from her company."

The Westchester County medical examiner's office found that Diane Schuler, 36, had a blood alcohol level of .19 percent -- more than twice the legal limit -- and had marijuana in her system when she drove a minivan the wrong way on the Taconic State Parkway and ran head-on into an SUV.

Three adults in the SUV were killed in the July 26 crash, along with Schuler and four children in her minivan -- her daughter and three nieces. A fifth child, Schuler's son, survived and is in stable condition.

Ruskin, a former officer in New York Police's narcotics division, said he is hesitant to fully accept the autopsy report.

"I'm not saying the autopsy is wrong or right. I don't know if she smoked pot weeks prior. Marijuana stays in your system for up to 30 days," he said.

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The medical examiner's office released a statement on August 6, saying it stands by its autopsy results, and reiterated that Sunday.

Schuler's family expressed shock when the details were revealed, saying she had no history of substance use.

"There's no way she'd do this," Jay Schuler, Schuler's sister-in-law, said earlier this month. "She was responsible."

Tests revealed that Schuler had an additional six grams of alcohol in her stomach that had yet to be metabolized, according to Maj. William Carey of the New York State Police.

A vodka bottle was also found in the vehicle after the crash.

Ruskin is adamant that it is necessary to go back through the day of the crash.

"We are analyzing all of the data that we have to date. We have a staff that has consumed themselves with this case," he said. "We are trying to determine what happened here."

Schuler's husband, Daniel, "would like to remind people that no matter what happened here he lost his wife, his daughter, his nieces and he also grieves for the Bastardi and Luongo families," Ruskin said, referring to the other crash victims.